Dirk Kuyt's late second half winner was enough to give the home side all three points at the Nieuw Galgewaard Stadion.
Ronald Koeman's side, who put in an excellent performance in the Champions League with a 1-1 draw at Arsenal last week, had no answer to their mid-table opponents on Sunday.
The match ended in sour fashion with both sides each having a man sent off with five minutes remaining.
Utrecht's Patrick Zwaanswijk and Ajax's Andy van der Meyde were given their marching orders for fighting.
The result leaves Ajax seven points back of PSV while Utrecht sit just above the mid-way point in the Dutch table.
Feyenoord moved to within four points of second place Ajax with a convincing 4-1 victory over struggling Groningen at De Kuip.
The Rotterdam side scored three first half goals in the space of seven minutes, with a brace from Pierre van Hooijdonk followed by a third from Australian international Brett Emerton.
Thomas Buffel made it four nine minutes after the break and the visitors had to settle for a late solitary reply from Sander van Gessel with eight minutes remaining but it was not enough in the end.
Groningen drop a place to second bottom in the table after Zwolle picked up three big points with a 2-1 victory over RKC Waalwijk at the Oosterenk Stadion.
Marino Promes gave Zwolle a 1-0 half-time lead but RKC pulled themselves level three minutes after the hour mark through Jochen Janssen.
However a minute after the visitors made it 1-1, Jhon van Beukering scored the all-important winner to take the home side up a place to third bottom - three points behind Excelsior.
Click below for match stats:
Eredivisie:
Zwolle 2-1 RKC Waalwijk
Feyenoord 4-1 Groningen
Utrecht 1-0 Ajax
Click here for an updated Eredivisie table.
